U.S. patent number 5,619,957 [Application Number 08/611,345] was granted by the patent office on 1997-04-15 for method for controlling a cooling circuit for an internal-combustion engine.
This patent grant is currently assigned to Volkswagen AG. Invention is credited to Karsten Michels.
United States Patent |
5,619,957 |
Michels |
April 15, 1997 |
**Please see images for:
( Certificate of Correction ) ** |
Method for controlling a cooling circuit for an internal-combustion
engine
Abstract
A method for controlling a cooling circuit of an internal
combustion engine which includes a coolant pump for adjusting a
coolant flow rate, a radiator in which heat is exchanged between
the coolant and an air flow which can be controlled by a fan, and a
control unit which controls at least the speed of the coolant pump
and of the fan as a function of a required temperature value of the
coolant. In order to minimize the power consumption of the pump and
of the fan while maintaining an optimum coolant temperature, the
speed of the coolant pump and the speed of the fan are controlled
based on a comparison of the time efficiencies of the coolant pump
and of the fan for the heat flow transmitted to the radiator.
Inventors: |
Michels; Karsten (Braunschweig,
DE) |
Assignee: |
Volkswagen AG (Wolfsburg,
DE)
|
Family
ID: |
7755954 |
Appl.
No.: |
08/611,345 |
Filed: |
March 6, 1996 |
Foreign Application Priority Data
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Mar 8, 1995 [DE] |
|
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195 08 102.1 |
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Current U.S.
Class: |
123/41.44;
123/41.12 |
Current CPC
Class: |
F01P
7/048 (20130101); F01P 7/164 (20130101); F01P
3/20 (20130101); F01P 7/167 (20130101); F01P
2023/08 (20130101); F01P 2025/30 (20130101); F01P
2025/32 (20130101); F01P 2025/62 (20130101); F01P
2025/64 (20130101); F01P 2025/66 (20130101); F01P
2031/30 (20130101); F01P 2037/02 (20130101); F01P
2060/04 (20130101); F01P 2060/045 (20130101); F01P
2060/08 (20130101) |
Current International
Class: |
F01P
7/04 (20060101); F01P 7/00 (20060101); F01P
7/16 (20060101); F01P 7/14 (20060101); F01P
3/20 (20060101); F01P 005/10 () |
Field of
Search: |
;123/41.44,41.1,41.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0054476 |
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Jun 1982 |
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EP |
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0557113A2 |
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Aug 1983 |
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EP |
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2384106 |
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Oct 1978 |
|
FR |
|
3024209 |
|
Jan 1981 |
|
DE |
|
3439438 |
|
May 1985 |
|
DE |
|
3810174 |
|
Oct 1989 |
|
DE |
|
4238364 |
|
May 1994 |
|
DE |
|
58-074824 |
|
May 1983 |
|
JP |
|
2149084 |
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Jun 1985 |
|
GB |
|
8400578 |
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Jul 1983 |
|
WO |
|
Primary Examiner: Kamen; Noah P.
Attorney, Agent or Firm: Brumbaugh, Graves, Donohue &
Raymond
Claims
I claim:
1. A method for controlling a cooling circuit of an internal
combustion engine having at least one coolant pump for controlling
the rate of flow of coolant in the coolant circuit, a radiator in
which heat is exchanged between air passing through the radiator
and coolant in the radiator, a fan for controlling the flow of air
through the radiator, and a control unit for controlling the speed
of the coolant pump and the speed of the fan as a function of a
required temperature of the coolant comprising the steps of
determining the heat transfer time efficiencies in the radiator for
coolant circulated through the radiator by the coolant pump and air
driven through the radiator by the fan and controlling the speed of
the coolant pump and the speed of the fan as a result of the heat
transfer efficiency determination.
2. A method according to claim 1 including the step of determining
the coefficient of heat transfer for the heat flow rate into and
out of the radiator and forming partial derivatives from this
coefficient of heat transfer as a measure of the time efficiency on
the basis of the coolant flow rate produced by the coolant pump and
on the basis of the air flow rate produced by the fan.
3. A method according to claim 2 including the steps of determining
the power input required to produce the necessary coolant flow rate
and the necessary air flow rate based on the time efficiencies of
the coolant pump and of the fan for the heat flow transmitted to
the radiator and obtaining comparison values to determine the most
efficient control of the coolant pump and of the fan.
4. A method according to claim 3 including the steps of storing in
the control unit the power which has to be applied to the coolant
pump as a function of the coolant flow rate to be produced.
5. A method according to claim 3 including the step of storing in
the control unit the power which has to be applied to drive the fan
as a function of the air flow rate to be produced and of the speed
of movement of the motor vehicle.
6. A method according to claim 1 including the step of controlling
the coolant pump and the fan based on a comparison of the time
efficiencies for the heat flow rate to the radiator only after the
coolant has reached a low temperature limit.
7. A method according to claim 6 wherein the low temperature limit
is a temperature value attained at the end of a warming-up phase
after the internal combustion engine has been started.
8. A method according to claim 6 including the steps of controlling
the coolant flow rate produced by the coolant pump when the coolant
temperature is below the low temperature limit and no air flow is
produced by the fan so as to maintain a selected temperature
difference of the coolant at a coolant inlet and at a coolant
outlet of the internal combustion engine.
9. A method according to claim 1 including the steps of controlling
the coolant temperature until the required coolant temperature
value is reached by controlling coolant flow through a radiator
bypass by a temperature-dependent valve having a controllable cross
section and controlling the speed of the coolant pump or the fan by
a determination of the time efficiency for the heat flow rate as a
function of the required temperature.
Description
BACKGROUND OF THE INVENTION
This invention relates to methods for controlling a cooling circuit
for an internal combustion engine, in particular of a motor
vehicle, in which the cooling circuit has at least one coolant pump
for controlling coolant flow and a radiator in which heat is
exchanged between the coolant and an air flow which can be
controlled by a fan and wherein the speed of the coolant pump and
the speed of the fan may be controlled as a function of a required
temperature value of the coolant.
An arrangement for controlling the coolant temperature of an
internal combustion engine for use in a motor vehicle is described
in German Offenlelegungsschrift No. 38 10 174 in which the internal
combustion engine is connected by separate coolant pipes to a heat
exchanger in the form of a radiator and to a coolant pump. The
coolant circuit is completed by a coolant connecting pipe between
the heat exchanger and the coolant pump. A controllable-speed fan
for producing an air flow through the heat exchanger is associated
with the heat exchanger. In addition, that arrangement includes a
control unit which controls both the coolant pump for circulating
the coolant and the fan for producing the air flow through the heat
exchanger as a function of a variable required temperature value of
the coolant. In this system, the operating parameters of the
internal combustion engine are taken into account in the
determination of the variable required temperature value.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
method for controlling a cooling circuit for an internal combustion
engine which overcomes disadvantages of the prior art.
Another object of the invention is to provide a method for
controlling a cooling circuit for an internal combustion engine in
which the power consumption of the coolant pump and of the fan is
minimized while maintaining an optimum coolant temperature.
These and other objects of the invention are attained by
determining the heat transfer efficiencies of the coolant pump and
the fan for heat transferred to the radiator and controlling the
speed of the coolant pump and the speed of the fan as a result of
those determinations.
According to a preferred embodiment of the invention, a coefficient
of heat transfer for the heat flow transmitted to the radiator is
determined for this purpose. The partial derivatives of this
coefficient of heat transfer, which depends mainly on the
coefficient of heat transfer from the coolant into the material of
the radiator and on the coefficient of heat transfer from the
radiator into the air flowing through it, are determined on the
basis of the coolant flow produced by the pump and on the basis of
the air flow produced by the fan, as a measure of the time
efficiency of the water pump and of the fan.
Both the power to be applied to the coolant pump as a function of
the coolant flow produced thereby and the power to be applied to
the fan to produce a specific air flow through the radiator, as a
function of the speed of movement of the motor vehicle, are stored
in a control unit and are used for the determination of the heat
transfer efficiencies.
According to another aspect of the invention, a low temperature
limit for the coolant is selected which preferably marks the end of
the warming-up phase of the internal combustion engine and the
operation of the coolant pump and the fan are controlled as a
function of the comparison of the heat transfer efficiencies for
the heat transmitted to the radiator only after the coolant has
reached this low temperature limit. Below this temperature limit,
the coolant pump produces only enough coolant flow to maintain a
predetermined coolant temperature difference between the coolant
inlet to the internal combustion engine and the coolant outlet.
The coolant circuit may also have a second flow path which bypasses
the radiator. In this case the coolant temperature is adjusted
during warming up, until the low temperature limit is reached, by
controlling the flow through the second flow path, which has a
variable cross section. The control is preferably implemented by a
temperature-dependent valve, for example a thermostat. When the low
temperature limit is exceeded, the operation of the coolant pump
and of the fan are controlled as a function of the required
temperature value by a comparison of their heat transfer
efficiencies, in order to maintain the required temperature
level.
BRIEF DESCRIPTION OF THE DRAWINGS
Further objects and advantages of the invention will be apparent
from a reading of the following description in conjunction with the
accompanying drawings in which:
FIG. 1 is a schematic illustration showing a representative
embodiment of a coolant circuit according to the invention;
FIG. 2 is a flow chart illustrating a typical procedure for the
method of the invention;
FIG. 3 is a flow chart illustrating a typical procedure for the
control method during the warming-up phase of the internal
combustion engine; and
FIG. 4 is a flow chart illustrating a typical procedure for the
control of the coolant temperature during normal engine
operation.
DESCRIPTION OF PREFERRED EMBODIMENTS
The representative embodiment of a coolant circuit which is shown
in FIG. 1 includes an internal combustion engine 1 of a motor
vehicle and a plurality of pipes a-f having internal openings with
a cross-section which can be controlled by a temperature-dependent
thermostat valve 6. The circulation through these pipes of the
coolant which is driven by a coolant pump 3 is indicated by arrows
adjacent to the pipes. The pipe a leads from the engine 1 to a
radiator 2 in which the coolant emerging from the engine 1 is
cooled. For this purpose, air is drawn in from outside the motor
vehicle by a fan 4 which is mounted behind the radiator 2. As the
air passes through the radiator 2, heat is exchanged between the
air flow m.sub.l, which can be controlled by the fan 4, and the
coolant flow m.sub.w Furthermore, the pipe b, which bypasses the
radiator, has a cross section that can be controlled by the
temperature dependent valve 6 in order to control the coolant
temperature. The pipe c includes an expansion tank 7 and is used to
regulate the pressure in the entire coolant circuit. The pipe d is
connected to a heat exchanger 8 for heating the interior of the
motor vehicle, and coolers 9 and 10, for cooling the engine oil and
the transmission oil respectively, are arranged in the additional
pipes e and f. The pipes d-f are optional since the corresponding
cooling and heating functions can also be achieved in other
ways.
Furthermore, the coolant system also includes a control unit 5,
which may be the control unit for the internal combustion engine.
The control unit receives, as an input signal, the output signal
S.sub.sen of a temperature sensor 11 which detects the coolant
temperature .theta..sub.w,act at the engine outlet and it produces
output signals S.sub.pump, S.sub.air and S.sub.therm, to control
the speed of both the coolant pump 3 and the fan 4 and also
controls the temperature-dependent valve 6.
The following is a description of the control method which is to be
carried out by the control unit 5 for the coolant circuit. FIGS.
2-4 show flow charts for this control method by way of explanation.
As shown in FIG. 2 three phases V1, V2 and V3, are distinguished in
the method according to the invention: V1 is effective during the
warming-up phase of the internal combustion engine; V2 is effective
during driving with a normal operating temperature of the coolant;
and V3 is effective during the cooling down phase. In the first
method step A1, a check is carried out to determine whether the
internal combustion engine 1 has been started. If this is the case,
a comparison is made to determine whether the actual coolant
temperature .theta..sub.w,act at the engine outlet, as indicated by
the output signal S.sub.sen of the temperature sensor 11 is below a
low temperature limit .theta..sub.w,warming which is selected to
correspond to the end of the warming-up phase V1. If the coolant
temperature .theta..sub.w,act has reached the temperature limit
.theta..sub.w,warming, the coolant circuit is controlled in
accordance with the algorithm for phase V2 for driving at the
normal coolant operating temperature.
If the internal combustion engine 1 has not been started, a check
is carried out to determine whether the coolant temperature
.theta..sub.w,act exceeds a high coolant temperature limit
.theta..sub.w,cooling, which indicates that the engine 1 must be
cooled further. In this case, the coolant circuit is controlled
using an algorithm for the cooling-down phase V3. If the coolant
temperature .theta..sub.w,act falls below the high temperature
limit .theta..sub.w,cooling, control of the cooling system stops
until the internal combustion engine 1 is started again.
In the sequence of steps for the warming-up phase V1, which is
illustrated in FIG. 3, a comparison of the coolant temperature
.theta..sub.w,act at the engine outlet with a selected initial
coolant temperature valve .theta..sub.w,start is carried out as the
first step. If the coolant temperature is below the selected
initial coolant value .theta..sub.w,start, the coolant pump is
started after a delay lasting for a time period t.sub.start. This
delay keeps the heat flow from components of the internal
combustion engine 1 into the coolant as low as possible and thus
achieves faster warming-up of the components. After that time
period t.sub.start has elapsed, or the initial coolant temperature
value .theta..sub.w,start has been reached, the coolant flow rate
m.sub.w produced by the coolant pump 3 is increased continuously,
until the minimum coolant flow rate m.sub.w,win for maintenance of
the required temperature difference value
.DELTA..theta..sub.w,eng,req between the engine inlet and outlet is
achieved for the first time. The drive signal S.sub.pump,min for
the coolant pump 3 is calculated in the control unit 5 from the
minimum coolant flow rate m.sub.w,win. Once the minimum coolant
flow rate m.sub.w,win has been reached for the first time, the
operation of the coolant pump 3 is controlled by a drive signal
S.sub.pump,warming in order to maintain the required temperature
difference value .DELTA..theta..sub.w,eng,req of the coolant at the
intake and outlet of the engine. The actual temperature difference
value .DELTA..theta..sub.w,eng,act which is required for control
results from the rate of heat flow Q.sub.eng from the internal
combustion engine into the coolant, which is in turn calculated
from the instantaneous coolant flow rate m.sub.w, the instantaneous
engine load L.sub.eng and the engine speed n. The calculated heat
flow rate Q.sub.eng is preferably stored in the control unit 5 as a
performance graph for the specific internal combustion engine
1.
After the minimum coolant flow rate m.sub.w,win has been reached,
the coolant pump 3 should be prevented from reacting to brief
engine load and speed changes. Since brief changes in the engine
load L.sub.eng and the engine speed n are irrelevant for the heat
flow rate Q.sub.eng into the coolant because of the thermal inertia
of the internal combustion engine 1, inclusion of the speed of the
coolant pump 3 would result in unnecessary power consumption. The
drive signal S.sub.pump for the coolant pump is thus given a
dynamic transfer function whose time constants T.sub.stg are
selected such that the time response of the coolant pump
corresponds approximately to the response of the heat flow rate
Q.sub.eng from the internal combustion engine into the coolant.
The fan is not driven during the warming-up phase V1. Consequently,
except for any air flow produced by motion of the vehicle, no air
flow rate m.sub.l, passes through the radiator 2. The warming-up
phase V1 is complete when the instantaneous coolant temperature
.theta..sub.w,act reaches the low temperature limit
.theta..sub.w,warming for the first time.
As shown in FIG. 4, after the coolant temperature reaches the low
temperature limit .theta..sub.w,warming, the coolant temperature is
also controlled as a function of a required coolant temperature
value .theta..sub.w,req in accordance with the algorithm for
driving at the operating temperature during the driving phase. The
required temperature value .theta..sub.w,req is calculated first.
For this purpose the control unit 5 has a stored performance graph
in which the optimum required temperature value .theta..sub.w,req
for the predetermined engine temperature is stored for a variable
engine load L.sub.eng, engine speed n and coolant flow rate
m.sub.w. The control temperature .theta..sub.w,therm for the
temperature-dependent valve 6, from which temperature the drive
signal S.sub.therm for the temperature-dependent valve 6 is
determined, results from this variable required temperature value
.theta..sub.w,req at the engine outlet, the coolant flow rate
m.sub.w and the heat flow rate Q.sub.eng from the internal
combustion engine 1 into the coolant. In the same way as in a
conventional cooling circuit, the valve 6 controls the coolant
temperature .theta..sub.w,act by controlling the coolant flow
relationships between the pipe a, which leads to the radiator 2 and
the radiator bypass pipe b.
The calculation of the minimum coolant flow rate m.sub.w,win
produces the required minimum speed for the coolant pump 3 and thus
the optimum drive signal S.sub.pump,min. If the instantaneous
coolant temperature .theta..sub.w,act exceeds the required
temperature value .theta..sub.w,req at the engine outlet by a
difference value .DELTA..theta..sub.w,hot, then either the speed of
the coolant pump 3, and thus the coolant flow rate m.sub.w, or the
speed of the fan 4, and thus the air flow rate m.sub.l, is
increased. A time comparison of the efficiencies of the coolant
pump 3 and of the fan 4 for heat dissipation at the radiator 2 is
carried out in order to determine whether it makes more sense in
terms of power to change the speed of the coolant pump 3 or of the
fan 4. The heat dissipation of the heat flow Q.sub.w,k at the
radiator 2 depends on the coefficient of heat transmission k, which
is obtained from the coolant/radiator and radiator/air coefficients
of heat transfer, and is calculated in accordance with the formula:
##EQU1## in which A.sub.k is the area of the radiator 2 and
a.sub.k, b.sub.k and c.sub.k are constants for the calculation of
the coefficient of heat transmission.
In order to assess the effectiveness of changing the air flow rate
m.sub.l and the coolant flow rate m.sub.w, the partial derivatives
are formed: ##EQU2##
The magnitude of the increase in heat dissipation per unit mass of
the materials involved is thus obtained for each operating point of
the radiator. If these values are now compared with the power
inputs P.sub.L and P.sub.wapu which are required to provide the
necessary coolant flow rate and air flow rate, respectively, a
comparison value K.sub..eta. is obtained for assessment of the most
favorable operating point change. ##EQU3## If the comparison value
K.sub..eta. .gtoreq.1, then in terms of efficiency it is more
favorable to increase the air flow rate m.sub.l. If K.sub.72
.ltoreq.1, the coolant flow rate m.sub.w should be increased. If
the coolant circuit through a cooler 9 is used in order to cool the
engine oil as illustrated in FIG. 1, the instantaneous oil
temperature .theta..sub.oil can be monitored using a sensor which
is not illustrated. If the instantaneous oil temperature
.theta..sub.oil exceeds a high temperature limit
.theta..sub.oil,limit, then the coolant temperature
.theta..sub.w,act is reduced step by step until the oil temperature
.theta..sub.oil falls below this high temperature limit. The
required coolant temperature is then set to provide the selected
engine temperature.
The dynamic control response to brief changes in the engine load
L.sub.eng in the engine speed n for the maintenance of the required
temperature difference value .DELTA..theta..sub.w,eng,req differs
from the response for the maintenance of the required temperature
value .theta..sub.w,req. The dynamic of control in accordance with
the required temperature difference value
.DELTA..theta..sub.w,eng,req corresponds to that for the warming up
phase V1. The dynamic control in accordance with the required
temperature value .theta..sub.w,req by variation of the valve flow
S.sub.them and of the speeds of the coolant pump 3 and fan 4 must
take place more rapidly. A design compromise must be found between
the optimum in terms of power and the desired temperature constancy
of the components of the internal combustion engine 1. For the
power analysis, it makes sense to ignore brief temperature changes
of the components as occur, for example, during overtaking. If the
optimization is made in the direction of temperature constancy of
the components of the internal combustion engine, then the reaction
to changes in the engine load can be used to carry out initial
control with respect to changing the coolant temperature
.theta..sub.w,act or the heat flow rate Q.sub.eng into the coolant.
If an engine operating point is set which would result in an
increased heat flow rate Q.sub.eng into the coolant, then colder
coolant can be pumped into the internal combustion engine by
controlling the temperature-dependent valve 6, which results in an
increased heat flow rate Q.sub.eng into the coolant and thus
smaller component temperature fluctuations. Furthermore, the
coolant flow rate m.sub.w or the air flow rate m.sub.l can be
increased in anticipation of such requirement. This is recommended
in particular if the valve 6 is not able to follow fast
changes.
Although the invention has been described herein with reference to
specific embodiments, many modifications and variations therein
will readily occur to those skilled in the art. Accordingly, all
such variations and modifications are included within the intended
scope of the invention.
* * * * *